The present invention relates to a portable tennis racket stringing machine, and more particularly, the present invention relates to a tennis racket stringing machine which enables a user to easily adjust the tension of strings installed through a head frame of a tennis racket.
Generally, a tennis racket essentially consists of a racket handle, a throat, a head frame and strings. A string which is also called a gut, serves as an energy center of the tennis racket. In other words, a string bed which is formed inside the head frame by installation of the strings through the head frame, is directly brought into contact with a tennis ball to hit the tennis ball. At this time, stroke energy which is generated by a tennis player, is transferred to the tennis ball via the strings.
A natural gut string and a synthetic string are mainly used in a tennis racket. In order to allow a tennis racket to be used under the best condition, the tension force on the strings must be adjusted to be suited to a particular player. Research has shown that four weeks after a string is installed through a head frame an elasticity loss reaches at the maximum 15% in the case of the natural gut string and 20% in the case of the synthetic string. After eight hours an elasticity loss reaches at the maximum 5% in the case of the natural gut string and 15% in the case of the synthetic string. Therefore, even though a string did not break, the string must be changed with a new one every three months, or every six months at the latest.
Also, in a tennis racket, it is, necessary to finely adjust the tension force of strings depending upon a situation. That is to say, by finely adjusting the tension force of strings relying upon a factor such as a season, a temperature, a court surface condition, or the like, it is possible to vary striking power of a string bed for a tennis ball.
Apart from the fact that, although strings of a tennis racket did not break, the strings must be changed with new ones every predetermined period of time, particularly, in the case of a professional tennis player, breakage of strings frequently occurs. When the strings are made of natural gut strings, the breaking of the strings occurs more frequently. Thus, in order to adjust the tension force of tennis racket strings so that the tension force is suited to a particular player, or in order to change a broken string, a tennis racket stringing machine is needed.
Referring to FIG. 1, there is shown a schematic perspective view illustrating a conventional tennis racket stringing machine. Since the conventional tennis racket stringing machine 100 must be constructed in such a way as to create high tension forces, it is usually a large-sized structure. Due to this, it is the norm that the tennis racket stringing machine 100 is located in a tennis shop. Hence, a problem is caused in that a tennis player must travel to the tennis shop so as to change a string or adjust the tension of the strings.
While the tension force of strings must be frequently and finely adjusted relying upon factors such as temperature, humidity, court surface condition, or the like, so as to produce optimum playing efficiency, it is inconvenient that a tennis racket user must leave a tennis court and visit a location which is equipped with a tennis racket stringing machine. This is time-consuming and causes annoyance to the tennis racket user.
Moreover, due to the fact that different tennis racket stringing machines are located in tennis shops, and are respectively configured in such a way as to apply different levels of tension force to the string, a stringing operation must be repeatedly performed through a multitude of times to adjust the tension force to that optimally suited to the user.
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a tennis racket stringing machine in which respective component elements are fabricated in such a way as to be capable of being assembled one with another to allow the machine to be carried around and conveniently used irrespective of time and place, and which provides a simple configuration with a reduced manufacturing cost.
Another object of the present invention is to provide a tennis racket stringing machine which enables the tension force of the strings to be adjusted and whereby the tennis racket to be used under optimum tension force suitable for each tennis player.
In order to achieve the above objects, according to one aspect of the present invention, there is provided a tennis racket stringing machine comprising: racket fastening means including a lower supporting plate on which a head frame of a tennis racket is seated and which has a larger length than the head frame so that the head frame of the tennis racket can be securely maintained on the lower supporting plate in a lengthwise direction of the lower supporting plate, a fixed projecting section which is disposed adjacent to one end of the lower supporting plate and functions to fasten one end of the head frame of the tennis racket, a movable section which is disposed adjacent to the other end of the lower supporting plate in such a way as to be capable of being moved along the lengthwise direction of the lower supporting plate and functions to fasten the other end of the head frame of the tennis racket, and a clamp which is located below the lower supporting plate in such a way as to rotatably support a center portion of the lower supporting plate; and tension force adjusting means brought into close contact with the head frame of the tennis racket and wherein it is separated from the racket fastening means, for adjusting the tension force of strings installed through the head frame, so that the strings can be held under optimum tension force.
According to another aspect of the present invention, the fixed section comprises a fixed shaft which has one end secured to the lower supporting plate and the other end projecting upward, a first upper auxiliary plate which is fitted around the fixed shaft, and a first butterfly nut which is threadedly locked to the other end of the fixed shaft.
According to another aspect of the present invention, the movable section comprises a pair of bent pieces which are formed by a pair of portions of the lower supporting plate which are partially cut and bent downward, a rotating bolt which is rotatably fitted through the pair of bent pieces in such a way as to be supported by the pair of bent pieces and to a circumferential outer surface to which a manipulating wheel is secured at a predetermined position, a movable body which is threadedly coupled with the rotating bolt so that the movable body can be moved along the lengthwise direction of the lower supporting, plate by rotation of the rotating bolt, a movable shaft which has one end secured to an upper surface of the movable body and the other end projecting upward, a second upper auxiliary plate which is fitted around the other end of the movable shaft, and a second butterfly nut which is threadedly locked to the other end of the movable shaft.
According to another aspect of the present invention, the movable section comprises a pair of guide rails which are formed at the other end of the lower supporting plate, a wheel receiving groove which is defined in the lower supporting plate adjacent to the pair of guide rails, a movable block which is assembled with the pair of guide rails so that it can be slid along the pair of guide rails in the lengthwise direction of the lower supporting plate, a movable bolt which has one end secured to the movable block and the other end extending in the lengthwise direction of the lower supporting plate in such a way as to be capable of being moved inward of the lower supporting plate, a manipulating wheel which is received in the wheel receiving groove and is threadedly coupled with the movable bolt so that the movable bolt can be moved along the lengthwise direction of the lower supporting plate by rotation of the manipulating wheel, a movable shaft which has one end secured to an upper surface of the movable block and the other end projecting upward, a second upper auxiliary plate which is fitted around the other end of the movable shaft, and a second butterfly nut which is threadedly locked to the other end of the movable shaft.
According to still another aspect of the present invention, the lower supporting plate is composed of a pair of lower supporting plate halves, a socket portion is defined in a first lower supporting plate half, and a plug portion which is fitted into the socket portion, is formed on a second lower supporting plate half.
According to yet still another aspect of the present invention, the tension force adjusting means comprises a string drawing section, a tension force adjusting section and a motor stopping section; the string drawing section including a squeezing plate which is brought into close contact with the head frame of the tennis racket, a squeezing rod which is coupled to the squeezing plate so that it is aligned with a string installed through the head frame, a string reel which winds up the string connected to the squeezing plate, and a motor for rotatably driving the string reel; the tension force adjusting section including a seesaw plate which has one end coupled to the squeezing rod so that the seesaw plate can be rotated about a center shaft, a coil spring which has one end secured to the other end of the seesaw plate, and a tension forcexe2x80x94adjusting dial which is connected to the other end of the coil spring; and the motor stopping section including a projection which is formed on a circumferential outer surface of the squeezing rod at a preselected position, and a limit sensor which is arranged on a moving path of the projection and functions to stop the motor when the projection comes into contact with the limit sensor.
In accordance with the features of the present invention, not only the tension force of tennis racket strings can be finely adjusted to a level which is desired by a user, but the entire structure of the tennis racket stringing machine is simplified, whereby the machine can be easily carried around and conveniently used irrespective of time and place, and it is possible to manufacture the tennis racket stringing machine at reduced cost. Portability of the tennis racket stringing machine according to the present invention is further improved by the fact that a lower supporting plate is composed of a pair of lower supporting plate halves.